The conventional processing of tomatoes to standard formulated products (sauce, juice and paste) consists of the following basic steps.
______________________________________ Seasonal Milling Heating ("breaking" the tomato) Finishing to remove skins and seeds reduce particle size Evaporation Aseptic filling Storage On demand Formulation Packaging ______________________________________
It in known that:
Yield of formulated tomato products (sauce, juice and paste) per tonne or raw tomato is a function of viscosity. PA1 Viscosity is a property imparted by the insoluble fraction of tomatoes. PA1 The insoluble fraction of tomatoes is cell wall tissue and is often loosely described as PA1 These are groups of as yet poorly defined compounds of large molecular size. PA1 During conventional processing it is well known that there is considerable loss of viscosity. PA1 This loss is reduced by "heating" the tomato before removal of skins and seeds (a process known in the industry as "breaking"). PA1 Heating denatures the enzyme responsible for loss of viscosity (polygalacturonase). The enzyme is heat resistant and high temperatures are required. PA1 Polygalacturonase is present throughout the cell walls even in immature tomato fruits. PA1 i) slicing the fruit, PA1 ii) passing the sliced fruit in counter current with an aqueous liquid in a counter current extractor, the liquid being at a temperature such that the fruit slices are heated to a temperature of at least 65.degree. C., PA1 iii) recovering a liquid phase from the lower end of the counter current extractor and a solid phase from the upper end of the counter current extractor, PA1 iv) subjecting the solid phase to a finishing process to remove skins and/or seeds therefrom, and PA1 v) dewatering the finished solid phase to increase the viscosity thereof. PA1 i) Aroma, PA1 ii) Flavour, and PA1 iii) Colour and viscosity
Cellulose PA2 Hemicellulose, and PA2 Pectins or proto-pectins
It is not yet properly understood how the activity of polygalacturonase is triggered in whole mature fruit to denature the cell walls and soften the fruit.
One possible reason that polygalacturonase does not immediately break down pectins in the cell wall during maturation is the presence of calcium bridges in the molecular structure of the pectins. The Ca bridges inhibit the action of the enzyme. The polygalacturonase is an endopectolytic enzyme which splits the large pectin molecules internally breaking them down into smaller poly or oligo galacturonic acid units but not to single galacuturonic acid molecules.
During conventional processing the fruit is milled macerating the cell walls and disrupting cell structure. Organic acids (notably malic and citric acids) which are isolated from the cell wall in the organised cells of whole fruit are now brought into contact with cell wall material.
There is some evidence to suggest that citric acid (a strong chelating agent) chelates the calcium away from the pectin molecules removing the barrier to polygalacturonase activity. In these circumstances loss of viscosity is extremely fast, significant losses occurring in microseconds.
It is known that temperatures of 70.degree.-75.degree. C. will denature polygalacturonase in tomatoes. However, due to limitations in heat transfer, milled tomatoes heated to this temperature will lose significant viscosity because of the high activity of the enzyme during heat up. Such products are of high quality in flavour and colour and are termed "cold break". On the other hand if milled tomatoes are heated to 95.degree.-100.degree. C. (hot break) denaturing of enzymes is quicker and higher viscosity results along with some loss in quality of flavour and colour.